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We have had several quotes from different HVAC contractors in our area. I have 3 separate proposals all saying we needed a 3 ton system. I then called the person that installed the furnace and he said, we need a 3.5 ton unit. He was a trane dealer and recently did the install of the furnace on the home. I also had another Trane dealer come here and spent an hour measuring our home and determined we needed a 2.5 ton unit. I'm confused that there would be such a discrepancy and don't have a clue what to do. I have tried to get some referrals from people but being new to the area, we don't really know anyone. This is a new 2000 square foot home in Beaverton, Oregon.

1. What can happen if we don't install the right size unit?
2. Would it make sense to just install a 3 ton unit?

Your area (Portland, OR) is neither very hot nor very humid. I doubt that a new home there with 2,000 square feet of conditioned space would need more than 2 tons unless it is poorly constructed/sealed/insulated or has an unusual amount of glass on the east or west sides.

Why not go with the Trane dealer who spend an hour measuring your home? If he will do that, don't you suppose he will take whatever time is necessary to install your system properly?

If a system is too large (assuming proper installation in the first place) it will cycle on and off too much. This leads to discomfort and wears out the system sooner. And when you have humid weather, it won't remove the humidity as well as a smaller system that has longer run times.

Furthermore, it is essential that the duct system be large enough for the air conditioner and that the blower on the furnace be sized correctly for it. Sometimes it may be best to go up or down a 1/2 ton or so to get the air flow right. If your furnace has a 3-ton blower on it, a 2.5 ton condensing unit should work just fine.

I've yet to see a residential system that is undersized. If a system won't keep the house cool, it is always because of faulty installation or improper charge.

Whatever you get MAKE SURE IT HAS A THERMOSTATIC EXPANSION VALVE (TXV). Don't let anyone talk you out of one.

Originally posted by splitbolt I'm going to put it to you this way: my own personal experience is that I am pulling dead Goodman and Payne systems out all of the time, and I never replace them with the same brand. When I pull out a dead Trane, I'm almost always putting another new Trane back in.

I use to install Amana's exclusively earlier in my career, and I like them, but I've relocated since to an area Amana is hardly seen, so I can't comment on logitivity there.

People will line up to tell you it matters highly on the quality of the install, which is entirely true, but even then I don't believe all units are equal.

Yep. The guy that spent an hour measuring is the one that took the time to do the real calculations for the correct system size. As usual, the one who measures and calculates using Manual J ends up quoting the smallest tonnage system. He's the winner, any day of the week. Everyone else just guesstimated.

The reason he's more expensive is because 1) Trane equipment is more expensive than the other brands quoted, 2) Trane 12-seer costs more than Trane 10-seer, and 3) he's the one that's going to do the best installation work and provide the best results. If the $700 difference worries you that much, ask him what his price would be for a 10-seer system instead of the 12.